Following his blacklisting in 1950, Koch used the pseudonym Peter Howard to write the British-produced "Finger of Guilt" (1956), directed by fellow exile Joseph Losey under the pseudonym Joseph Walton.Koch retired to Woodstock, NY where he remained actively involved in local theatre, writing and producing plays. He died of pneumonia at age 93 in August 1995. The following December, Koch's Oscar for "Casablanca" was sold at auction by Christie's for $184,000.